1. Field of the Invention
The invention relates to a method and the appertaining devices for aerobically fermenting organic materials, preferably agricultural and foodstuff waste products, including excrement, and simultaneously producing heat and high-grade biologically and hygienically acceptable fertilizer.
Such methods and the appertaining technical devices serve the purpose of decomposing--in an economical and environmentally acceptable manner--waste products resulting from agriculture and forestry, vegetable production and horticulture, landscape and part maintenance, as well as excrement, and the like, by means of aerobic fermentation, and of simultaneously producing a good fertilizer, as well as heat for heating purposes, or the like. There are extensive, many-sided and economically significant tasks here, specifically: to eliminate wastes from agriculture, timber and forest cultivation and from foodstuff, as well as, e.g., the great quantities of mowed material from road, park and landscape maintenance, and the like, in a more advantageous manner; to convert the great quantities of animal excrement--and to some extent also human excrement--in an environmentally acceptable manner so as to be free of harmful germs; that is, to produce a hygienically acceptable, biologically high-grade fertilizer for use in agriculture and forestry, vegetable production and horticulture, and as commercial goods in moist and dry form; and to obtain heat in these decomposition processes, wherein all methods must be carried out economically, in an environmentally acceptable manner and without objectionable odor for the population.
2. Discussion of the Prior Art
Very many individual suggestions have aleady been proposed in this regard; however, they are either not universal enough or are too costly in terms of money and energy or are not environmentally acceptable. In agriculture, particularly in large-scale animal maintenance, the excrement increasingly poses a particular problem, since the great quantities of the latter can only be employed partially--and not at all in strictly large-scale animal maintenance enterprises, such as chicken farms--for fertilizing the surfaces of one's own enterprise. Moreover, various rationalization measures, such as liquid waste removal, have as consequence that the agricultural animal excrement results to an increasing degree in pumpable form as liquid manure; however, in liquid manure fertilization, the dissolved components are easily washed out and lead to contamination of the groundwater and the receiving water. The strong odor, particularly from fowl and pig liquid manure, leads to severe odor problems for the residents in residential areas. The problem of hygiene also takes on increasing significance in continuous, heavy liquid manure fertilization: e.g., it is known that salmonella in liquid cow manure is not destroyed even after yearlong storage.
In the forefront of the efforts to solve the problems in the economical and ecological sense is the processing of the resulting organic products and excrement in such a way that economical methods are applied, on the one hand, for supplying one's own operations with fertilizer and, on the other, for producing a salable commercial fertilizer from the raw products when there is a surplus, whereby no additional environmental load may occur and the products are hygienically acceptable and the foodstuff is stabilized. Thus, for example, moist compost or other moist substrates are very well suited as commercial fertilizer. The only disadvantage is that the latter must be used relatively quickly, since, in the moist state, a gradual loss of weight and volume results through continued biological decomposition. Also, the moist compost has a large weight and, as commercial fertilizer, has disadvantages due to high transportation costs and its storage and transportation is connected with high costs. Therefore, it is advantageous if the commercial fertilizer produced from surpluses is in dry form. Only a lengthy fermentation process in the mesophilic temperature range over 40.degree. C. or a brief hot fermentation of at least 4 days at temperatures over 65.degree. can achieve the required hygienic level. The disadvantage of carrying out these high temperatures through heating by means of commercially available means, such as oil, and the like, is the high cost in energy. Moreover, excessive drying temperatures cause considerable losses in volatile nitrogen compounds. Aeration treatment of liquid manure also causes excessive costs and losses in foodstuff without being able to put the product into commercial form.
A series of suggestions have already been made to overcome these problems. Various attempts have also been made to convert solid waste, particularly from large-scale animal maintenance, e.g., poultry excrement, into commercial compost by means of composting on stacks. This lengthy stack composting requires repeated transferring, protection from rain or deliberate moistening, if too severely dried out, and a large surface area, which must under all circumstances be structurally secured, all of which brings about high costs in material and labor, so that this method cannot be instituted.
Natural or mechanical separation of solids, such as the removal of floating and sinking layers, filtering, screening or centrifuging, likewise cause high costs without meeting the above-mentioned strict conditions required for a commercial product.
An effective hot fermentation, with temperatures reliably over 65.degree. C. for at least 4 days, can only be achieved with exactly proportioned aeration of the fermentation stack. The stack must be circulated twice daily if possible during this period in order to bring the cooler outer layers into the area of the high temperatures as well. Naturally, this high expenditure in labor can be avoided in insulated throughflow mechanisms; but the costs for the expenditure in labor and for the mechanism are very high here as well.
Circulating mechanisms in the form of rotary drums or sliding grate mechanisms are already known. These mechanisms are very expensive due to the extensive mechanical aggregates, which must be protected against corrosion; they cannot be put into operation to any considerable extent in agriculture, or the like, because of the cost alone.
It has also already been attempted repeatedly to derive and make use of the heat from aerobic hot fermentation processes. The simplest way to derive the heat consists in conducting the forced aeration of the fermentation stack through heat exchangers. If large stacks are fermented in this manner in the mesophilic range to approximately 45.degree. C., then the method can indeed be carried out, but the heat can only be used to supply low-temperature heating systems because of the low temperature level. The stacks dry out easily, since, along with the heated air, considerable quantities of water are carried out of the stack. A recycling of the heat exchanger condensation product is very difficult because high technological expenditure is required to distribute it uniformly. The higher the stack temperature is maintained, e.g., to improve the hygienical process, the more difficult the problem of drying out or remoistening, respectively.
The derivation of heat from aerobic fermentation stacks by means of internally or externally located heat exchangers is impeded in that the layers of contact between the fermentation stack and the heat exchanger surfaces cool faster than the heat can be resupplied from the depth of the stack. The temperature can be up to 20.degree. C. higher at a distance of 20 to 30 cm from the immediate contact layer. However, with high stack temperatures of 65.degree.-75.degree. C., there is an advance running water temperature of only 40.degree. to 45.degree. in the heat exchanger, which is not sufficient for, e.g., supplying normal hot water heating systems.
It has also already been attempted to overcome these difficulties by providing relatively small exchanger surfaces in very large stacks, so that the heat flow in the direction of the heat exchanger can be improved, or by keeping the temperature drop between the stack and the heat exchanger slight. However, in both cases, the available heat capacity per quantity unit of the stack was so reduced that such systems were abandoned for reasons of cost.
The fermentation stack has also been circulated in such a way that it slides along the exchanger surfaces. This occurs in one type of system in that the fermentation material is repeatedly removed from beneath an index or register of surface heat exchangers and returned again from above. The cooled contact layers are thereby mixed in again; but the above-mentioned problems of not contacting the contact area can only be improved when the entire compost substance is continuously circulated as a whole with a considerable expenditure of energy. This requires a high expenditure of energy and these circulating systems are not suited for through-flow mechanisms because the material through-flow is constantly interrupted and must even be reversed.